Processing Raw in a 3rd Party Application
You can also process your Raw with a 3rd Party app like ACR or Photoshop. *But* iPhoto does not handle this gracefully and it's a bit of a kludge.
First off set your preferred app as an external editor in iPhoto:
You can set Photoshop (or any image editor) as an external editor in iPhoto. (Preferences -> General -> Edit Photo: Choose from the Drop Down Menu.) This way, when you double click a pic to edit in iPhoto it will open automatically in Photoshop or your Image Editor, and when you save it it's sent back to iPhoto automatically. This is the only way that edits made in another application will be displayed in iPhoto.
Note that iPhoto sends a copy+ of the file to Photoshop, so when you save be sure to use the Save command, not Save As... If you use Save As then you're creating a new file and iPhoto has no way of knowing about this new file. iPhoto is preserving your original anyway.
Next: In the iPhoto Preferences -> Advanced, elect to use Raw with your External editor:
Now when you go to edit the Raw it will be sent to your external editor.
Now for the kludge:
You cannot save a Raw. The work you do must be output to a new file, in a new format (jepg, tiff, whatever). However, as the External Editor is making this new file iPhoto has no knowledge of its existence. Therefore you *must save it to the desktop and then import it back to iPhoto as a new file*.
This means that you will have your Original Raw and the processed version in iPhoto but they will not be recognised as version and original. iPhoto will see them as two separate shots.
